The present invention relates to vehicle navigation systems. More specifically, the present invention provides a method for identifying highway access ramps as locations for the calculation of routes using a vehicle navigation system. The present invention also provides a method and apparatus for determining a route based on the location of a highway access ramp using a vehicle navigation system.
In the map databases employed by today's vehicle navigation systems, different levels of detail are provided for different types of geographic regions. Metropolitan regions, which include urban and suburban areas, generally have a high level of detail and account for much of the detailed map information stored in the databases. By contrast, very little detail is provided for rural areas and outlying towns lying in the sparsely populated regions which interconnect metropolitan regions. These regions are referred to herein as highway regions. The term "highway" herein includes roads which meet several criteria discussed below and is used to describe, among other things, highways, freeways, and expressways.
When using a vehicle navigation system, a user typically selects a destination so that the system may calculate a route and provide guidance information to the destination. For example, if the user wishes to travel to a particular street intersection in an urban area, she may select the intersection as provided by the map database. The level of detail for urban areas provided by available map databases is generally such that most, if not all, street intersection information is available to users. However, because map databases do not provide detailed coverage of highway regions, many destinations in these regions are not available for route calculation.
The level of detail provided by available map databases for highway regions typically includes the highways themselves and the major roads to which they are connected. More detailed surface street information is generally not provided. Thus, the destinations to which users would most likely be heading in highway regions are usually unavailable for route calculation purposes. Therefore, there is a need to provide users of vehicle navigation systems with destination options in highway regions. Highway access points (i.e., on-ramps and off-ramps) are possible destination options, but available map databases do not provide information regarding such access points in a form which identifies them as such and which may be presented to the user as a destination option.
The availability of highway access points for route calculation and guidance would be advantageous in situations in which the user would like to find the nearest entrance to a highway, for example. Another situation in which the availability of highway access points for this purpose would be an advantage is where the user is familiar with the surface streets near her highway region destination and/or near her present location in an urban area. In such a case, she only needs to specify the highway exit near her highway region destination to receive sufficient route guidance.
In view of the foregoing, it is evident that there is a need to provide users of vehicle navigation systems with highway access points as destination options for the purpose of route calculation and guidance. The present invention meets that need.